The present invention relates to a fluid valve, and more particularly to a valve having different, or variable, settings for affecting flow of a fluid. In a preferred embodiment it relates to a fluid valve for damping a hydraulic assembly.
A number of devices in the prior art employ hydraulic or fluidic dampers or dashpots to smooth out mechanical motion or jitter. Vehicle shock absorbers are one example of such devices, and substantially similar devices are used for office chairs, door closers, and other applications. In several of these applications the device is subject to asymmetrical impulse actuations, or operates in a range of motion about a set point offset from its center. For example, a vehicle shock absorber may be subject to upward impulses in which energy is delivered in larger amounts, or during shorter time intervals, than the gravity- and spring-driven downward return movements.
Conceptually, a vehicle suspension generally includes a spring and a fluid damper. The spring elastically stores and returns the energy of up-and-down motion of a mechanical assembly such as the hub driving the wheel to smooth the sharp impacts caused by running over irregularities in the roadway and restore the suspension to a neutral position, while the damper dissipates a portion of the energy in each stroke or cycle to prevent resonant oscillations from arising. Energy dissipation is achieved by introducing frictional losses. This may be done by arranging that a piston connected to the suspension displaces hydraulic fluid through a flow impediment, e.g., one or more small orifices that introduce turbulence, drag. viscous shear or other lossy events in the fluid, which may for example be a liquid or a high pressure gas.
Practical implementation of such a mechanical damper entails considerations of the expected frequency and shape of displacement impulses, vehicle mass, the desired range of motion of the suspension, and the required strength and allowable weight of the damper assembly. For automobiles, suitable shock absorbers are achieved with piston-type assemblies located at each wheel, and each weighing two to ten kilograms, with a piston travel of about five to thirty centimeters. Smaller assemblies may be used on mechanisms such as steering arms or tailgate assemblies, while even larger ones may be necessary to accommodate heavy loads or driving on rough roadway surfaces.
When an assembly of this type is to be used for a mountain bicycle, weight is a primary consideration since the total vehicle weight must be pedaled by the user. Furthermore, the vehicle handling is strongly affected by the characteristics of the damper. The front suspension, e.g. a telescoping fork, is the steering mechanism, and impacts on the rear wheel may pass fairly directly to the seat, so both the comfort and actual steering aspects of handling are affected.
One known bicycle shock absorber employs a piston that displaces fluid within a hydraulically full and sealed cylinder. The piston has a number of passages extending between one side and the other, and each passage has a flexible washer fastened over one end to act as a one-way flap valve allowing flow in only the forward, or only the reverse direction. The number and sizes of these passages are configured to resist fluid displacement and thus control movement of the piston when the bicycle is subjected to changing terrain and impact. This construction is structurally strong and mechanically robust. However, because of the extreme range of conditions which a bicycle may experience, these shocks cannot operate optimally under some combinations of diverse conditions. When the passages are sized to resist flow of hydraulic fluid only weakly, a smoother or xe2x80x9csoftxe2x80x9d ride is obtained, but a large force will cause the shock to quickly xe2x80x9cbottom outxe2x80x9d and become ineffective. On the other hand, if the passages are configured to inhibit flow so much that the shock absorber never bottoms out under conditions of energetic impact, then the shock absorber provides a xe2x80x9chardxe2x80x9d ride, greatly reducing comfort. It is generally desirable to have a stiff suspension during pedaling, so that energy of pedaling is not lost to the suspension. However, between periods of pedaling, when there are moderate impacts, a softer ride is needed.
Accordingly, if would be advantageous to provide a flow valve having different characteristics suitable for controlling a range of expected flows occurring over a wide range of driving conditions.
It would be further advantageous to provide a flow valve with variable flow control or regulation characteristics which change to match existing conditions.
This is achieved in accordance with the present invention by providing a valve to regulate fluid displacement, for example of hydraulic fluid in a sealed shock absorber, wherein the valve is placed between a portion of the fluid at one pressure and controls fluid flow as the fluid is driven along a passage to a portion of fluid at a lower pressure. An aperture constitutes or communicates with the passage, and a blocking member is moved to obstruct the aperture in accordance with a desired level of damping. An electroactive device, such as an actuator formed of ferroelectric material, is actuated to position the blocking member.
In one embodiment, the blocking member is a bimorph which covers the aperture. The bimorph is deflected by passage of fluid through the aperture, and a controller provides an electrical activation signal to drive the bimorph toward or away from the aperture, augmenting or decreasing its closing bias. This affects both the threshold flow initiation pressure and the degree of flow permitted once the passage is opened. In other embodiments the aperture or passage may be a slot-like channel, with the blocking member positioned in the slot like a flap or reed. Actuation of the member bends it into the stream to affect flow. In other embodiments the passage may feed to a groove formed in a plate surface, and the blocking member covers the groove. Preferably the blocking member is a flexible piezoelectric assembly, which moves across a gap to provide a varying obstruction in the near field of fluid flow as the fluid moves through the passage. Piezobenders, washers and various pinned or cantilevered constructions adapt to different passage geometries.
In a presently preferred embodiment, a plenum attaches to a damper housing, and includes a first passage leading to one side, illustratively the top or high pressure side, of the damping piston, and a second passage connecting to the other, e.g., bottom or return pressure side of the piston. A piezo bender covers an elongated opening between the first and second passages and a controller moves the bender toward or away from the opening to reduce or increase flow along the first passage into the second passage. A position sensor connected to the controller senses piston position, and the controller operates to energize the bender and to obstruct the opening or further restrict flow if the piston position or velocity is determined to lie above a threshold. This extends the useful range of the damper and may allow optimal stroke of the damper during all conditions of use, enhancing comfort while preventing bottoming out and unnecessary loss of rider energy. Other passages with fixed one-way valves in each direction may be provided to tailor the general damping characteristics of the damper.